This invention relates to a knife shaft assembly for a document shredder, which is formed by a plurality of cutting disks arranged on a shaft with spacer rings between them.
Document shredders have as a rule two knife shaft assemblies whose cutting disks intermesh in contact with one another and which are driven to rotate in opposite directions. Documents fed in between the cutting disks are shredded. If the cutting disks are thin and contact one another on only one side where they cut the paper, it is important for trouble free operation that the disks be held tightly against one another and that the spacing of the cutting disks arranged on the knife shafts and held tightly against one another be the same on both knife shaft assemblies. Otherwise stresses occur between the two knife shaft assemblies resulting in increased friction, lowering the output of the document shredder, and making it impossible to assemble an effective cutting mechanism. On the other hand, dimensional variations may cause the cutting disks to fail to contact one another, so that no cutting occurs.
Any variations in the spacing between the cutting disks on the knife shafts can also lead to problems if one piece strippers are used with fixed spacing between the fingers as described, for example, in German Published Patent Application No. DE 36 16 554. In such a case, if there are dimensional differences between the cutting disks and the stripper, harmful friction will result, and in some cases it may even be impossible to assemble the cutting mechanism.
Inaccuracies in the knife shaft assemblies of the kind described can very easily result if the cutting disks are stamped and then ground from a material of slightly varying thickness. The same applies to the spacer rings which are usually made by turning. Over the length of the knife shaft assemblies, slight differences in the material thickness can be so great that the adverse effect described above can very easily occur. To prevent such undesirable inaccuracies it has heretofore been necessary to engage in a great deal of trouble and expense in selecting the material and in manufacturing the components.